One method of sputter-coating involves ion bombarding a target of the coating material in an ionized gas atmosphere in a chamber in which a controlled vacuum is maintained to cause atomic particles of the coating material to be dislodged and deposited by condensation on the substrates to be coated. The gas employed is a non-reactive or inert gas, such as argon.
However, many processes in vacuum deposition utilize a method known as reactive deposition where a pure metal or alloy target material is liberated from it's bulk and directed toward a substrate which is intended to collect the material as or after it has reacted with a gas which is present in the path of the liberated target material or at the substrate surface.
The reactive sputtering is often difficult to control, rates of deposition are erratic, arcing of the target occurs due to resistive film build up on the target face, and yields are often unpredictable.